According to Wikipedia, we know that color-vision photopigments appeared in the common ancestors of tetrapods and fish at least 360 MY ago. Would life have been less colorful before the evolution of color vision?

It's hard to know for certain, but probably. Color is used to signaling to mates, predators, hiding from prey and predators, etcetera. Life would not have been grey or brown, a lot of antioxidant pigments have color to them, but ladybugs/flowers/etc couldn't be as bright as they are now.
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ResonatingAug 14 '13 at 20:01

1 Answer
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It is likely that the world have been less colourful before colour vision evolved, though that is my opinion, I will now back it up a little.

Certainly some of the colour we see in nature serves a function outside of the use of visual stimuli. For example plants have green leaves because of the way that functions with photosynthesis - it absorbs enough energy whilst not so much that the leaves burn. For more on the green leaves in plants see this classic Biology SE question with it's very good answers. Other examples could include functions such as thermal regulation or light contrast for camouflage (if anyone has other valid examples then please comment and I'll add them in).

However, there is likely to have been an increase in the prevalence of colour in nature since the evolution of colour vision. Colour is used as a visual stimulus in numerous ways. My first example is flower colouration. Flowers use coloured petals as a stimulant to attract pollinators. Another example is the use of colour in mate attraction. Peacocks tails, the orange bills of blackbirds, and the brightly coloured cichlid fish. All of these examples take advantage of colour vision, without it they simply wouldn't be as discernible from less colourful variants and given the cost of producing them it is unlikely they would evolve as often as they do. A third example is camouflage, the most striking example I can think of is cuttlefish which match themselves very well to their background.

Although I haven't provided direct evidence that the world was less colourful I have provided a potential theory. Hopefully the examples I've presented have convinced you that my theory of the world being less colourful, even possibly only marginally less so, is not developed without thought.

I will point out it is entirely possible the world was equally or even more colourful before - no colour vision would allow colours to drift around more, selection on colour in the context of camouflage would reduce the variety of colour we see as selection would favour colours matching the surroundings (if camouflage was necessary to survival in a grass environment we would expect most things to look quite green). To this end, I don't think we can currently answer your question firmly but we can put out theories as to how it would have been.